I had a similar experience with a very well known manufacturer a few years ago. One .284 bullet in a box of .277. I was all wound up, figured they might need to issue a recall on that lot etc etc.
I called them and kindly pointed out their error. I was not looking for a reward as much as helping with my perceived safety issue. The lady on the phone was totally un-impressed. "Yeah, happens sometimes when a bullet gets stuck in the system and pops loose later" and "We will send you 5 bullets for your trouble"
Yes, 5. Of a different lot of course. Worthless to me. I had them sent and threw the original package in a drawer. Figured if some poor sapp made headlines and sued the manufacturer, his lawyer would really like me to take the stand.
Never happend. Moreoever, in hindsight, I think the manufacturer would win the law suit. You really should notice a larger bullet. Which the OP and I both did, it appears.